Tires for each specific type of vehicle must have a normal internal pressure corresponding to that specific type of vehicle. In the event the internal pressure of a tire (that is, the tire pressure) is too low or too high, it would have adverse influences on driving safety. Therefore, it is necessary to periodically or non-periodically check the tire pressure so as to ensure safe driving.
Tire pressure gage is an instrument for measuring tire pressure, and typically includes a housing forming a main body of the gage, and a measuring head formed at an end of the main body toward an air valve on a tire. The tire pressure gage is internally provided with a measuring stem having scales or graduations lengthwise provided thereon, and a spring. In measuring the tire pressure with the tire pressure gage, the scaled measuring stem projects outward from the main body by a different length, depending on the pressure inside the tire. From the scale corresponding to the projected length of the measuring stem, a measured tire pressure or a reading of the tire pressure is obtained. There is also a digital-type pressure gage on which a tire pressure reading in digits is directly shown on a display of the gage.
Since tires are located at the lowest part of a vehicle, the measuring of tire pressure is done in a relatively limited space. To facilitate easy measuring of tire pressure in a limited space, the tire pressure gage is usually designed to have a small volume, which also enables convenient carrying of the gage. The scales or graduations provided on the miniaturized tire pressure gage are also reduced in size to such an extent that they are not easily and clearly readable and as such, the measured tire pressure cannot be quickly caught sight. Moreover, the angular position of the air valve on the tire also hinders a user from easily and clearly viewing the reading on the tire pressure gage.